Over 700 naturally occurring .alpha.-amino acids have been discovered in nature and many more have been produced synthetically. Virtually all of them have some biological importance. Amino acids and their derivatives are increasingly being employed as chiral synthons, catalysts and auxiliaries in asymmetric syntheses. Since relatively few (2 to 3%) of the known amino acids occur abundantly in nature, most recent work has focused on their synthetic production in optically-active form. Currently, general methods for syntheses of amino acids often suffer from lack of stereochemical control, poor yields or numerous steps. Since both enantiomers of the proteinogenic amino acids serine are available at relatively low expense, they are especially attractive chiral synthons for other rare or unusual amino acids.
The 20 common (2S)-L-.alpha.-amino acids play a central role in the primary metabolism of all living organisms. A vast majority of the remaining naturally-occurring non-protein amino acids are generated by various plants and lower organisms as secondary metabolites, products of detoxification of foreign compounds, or as defense mechanisms against predators or competitors. Either free or as constituents in peptides or depsipeptides, the non-protein amino acids are responsible for an incredible spectrum of biological activities.
Pharmacologically the most important of these activities are their action as antibiotic and antitumor agents and as antimetabolites and hormone analogues for the treatments of various diseases. As a result, natural non-protein amino acids and their almost innumerable synthetic modifications function as important components in many drugs and pharmaceuticals. Importantly, all of the .alpha.-amino acids produced in nature are enantiomerically pure, and often each enantiomer displays a specific biological activity. In addition, with the emergence of peptide syntheses as a powerful tool in molecular biology there is an ever-increasing demand for a wide range of amino acids with high optical purity. Among other things one intention of this invention is to produce synthetically .alpha.-amino acids which are enantiomerically pure.